1. Field of the Invention
This invention relates to seals for valves and, more particularly, to seals for valves that have rotating stems.
2. Description of the Prior Art
The prior art is replete with various forms of valves and seals therefor; a number of which are directed to the resolution of the problem of maintenance and integrity of the stem seals which effect the rotating seal between the casing and valve stem.
In addition to the above noted problem area and also related thereto is the problem of providing a valve which can be readily maintained in a field environment and, more particularly, a provision of a valve which may be maintained without any interruption of the flow in the line with which it is associated. One of the more typical field maintenance tasks is the replacement of the stem seals and it is important that the valve continue to function at least temporarily while these seals are being replaced.
In addition to the above noted problems, there has been a continual need for the provision of a new and improved packing seal for valves having roting stems as contrasted to those having rising stems; particularly plug valves whose plug and coupled stem are rotated through a limited arc. The seals must have a number of characteristics to enable it to perform effectively in such an environment. For example, a stem seal in a plug valve environment should possess a substantial degree of lubricity to reduce friction with respect to the stem and also reduce the wear on the seals themselves. With respect to this latter point, the life of the seal can be extended substantially if the friction between it and the various moving parts of the valve with which it is associated can be reduced. Another important function of the seal is to maintain its own strength characteristics during its operational life. This particular feature of the seal becomes all the more important when it is compressed by a gland ring or the like.
Examples of typical prior art forms of valves in this general area and other art which may relate thereto are as follows: U.S. Pat. Nos. 1,584,699; 1,671,603; 1,680,812; 2,945,668; 3,096,070; 3,115,151; 3,231,235; 3,406,707; 3,537,682 and 3,586,289.